Hybrid distribution transformer with an integrated voltage source converter

1. A hybrid distribution transformer having a primary side for receiving input voltage and current from a source and a secondary side for providing output voltage and current to a load, the hybrid distribution transformer comprising: a ferromagnetic core; a winding structure for a power phase, the winding structure comprising one or more first windings and one or more second windings wound around the core, wherein the one or more first windings are disposed on one of the primary side and the secondary side of the transformer and the one or more second windings are disposed on the other one of the primary side and the secondary side of the transformer; and a single voltage source converter connected to the winding structure and operable to convert between DC and AC voltages, the voltage source converter comprising: at least one switching bridge comprising two or more switching devices; a DC bus connected in parallel with the at least one switching bridge; and a controller operable to control the at least one switching bridge to control the power factor on the primary side of the hybrid distribution transformer and to reduce variations in the output voltage in the event of a change in the input voltage.

2. The hybrid distribution transformer of claim 1 , wherein the one or more first windings comprises a single first winding and wherein the voltage source converter is connected in series with the first winding.

3. The hybrid distribution transformer of claim 2 , wherein the one or more second windings comprises a single second winding and wherein the first winding is a primary winding and the second winding is a secondary winding.

4. The hybrid distribution transformer of claim 2 , wherein the one or more second windings comprises a single second winding and wherein the first winding is the secondary winding and the second winding is the primary winding.

5. The hybrid distribution transformer of claim 2 , further comprising a voltage divider having an output connected between the voltage source converter and the first winding.

6. The hybrid distribution transformer of claim 1 , wherein the one or more first windings comprise a pair of first windings and wherein the voltage source converter is connected in parallel with one of the first windings.

7. The hybrid distribution transformer of claim 1 , wherein the one or more first windings comprises a single first winding, and wherein the first winding has opposing ends, a plurality of turns disposed between the ends and an inner tap connected to one of the turns, the inner tap helping define first and second winding portions of the first winding, and wherein the voltage source converter is connected to the inner tap of the first winding.

8. The hybrid distribution transformer of claim 7 , wherein the input voltage or the output voltage of the hybrid distribution transformer corresponds to the voltage across the first winding portion, and wherein the voltage source converter is connected across the second winding portion.

9. The hybrid distribution transformer of claim 8 , wherein the first winding is the primary winding.

10. The hybrid distribution transformer of claim 8 , wherein the first winding is the secondary winding.

11. The hybrid distribution transformer of claim 7 , wherein the input voltage or the output voltage of the hybrid distribution transformer corresponds to the voltage across an end or outer tap of the first winding portion and a node between two switching devices in a switching bridge of the voltage source converter.

12. The hybrid distribution transformer of claim 11 , wherein the first winding is the primary winding.

13. The hybrid distribution transformer of claim 11 , wherein the first winding is the secondary winding.

14. The hybrid distribution transformer of claim 1 , wherein the voltage source converter is an H-bridge inverter comprising first and second switching bridges connected in parallel with a DC bus.

15. The hybrid distribution transformer of claim 1 , wherein the voltage source converter is a half bridge inverter comprising a switching bridge connected in parallel with a DC bus.

16. The hybrid distribution transformer of claim 1 , further comprising sensors and an intelligent electronic device (IED) for monitoring the operation of the hybrid distribution transformer, the IED being connected to receive DC power from the DC bus and operable to receive operational data of the hybrid distribution transformer from the sensors, the operational data including currents, voltages and temperatures in the first and second windings.

17. The hybrid distribution transformer of claim 16 , wherein the IED comprises the controller and is connected to a remotely located control center by a communication link, the IED being operable to transmit the operational data to the control center and to receive commands for the controller from the control center.

18. The hybrid distribution transformer of claim 1 , further comprising a filter connected between the first winding and the voltage source converter, the filter being operable to suppress high frequency harmonics arising from the operation of the switching devices.

19. The hybrid distribution transformer of claim 1 , further comprising: a protection device connected between the voltage source converter and the one or more first windings, the protection device operatively disconnecting the voltage source inverter from the one or more windings in the event the voltage source converter malfunctions.

20. The hybrid distribution transformer of claim 19 , wherein the protection device is controlled by the controller and comprises first and second switches and an impedance, and wherein when a network fault is detected, the first switch opens and the second switch closes, thereby directing the fault current to the impedance.

21. A hybrid distribution transformer having a primary side for receiving input voltage and current from a source and a secondary side for providing output voltage and current to a load, the hybrid distribution transformer comprising: a ferromagnetic core; first, second and third winding structures, each comprising first and second windings wound around the core, wherein one of the first and second windings is a primary winding for connection to the source and one of the first and second windings is a secondary winding for connection to the load; and a voltage source converter connected to the first windings and operable to convert between DC and AC voltages, the voltage source converter comprising: a plurality of switching bridges connected in parallel, each switching bridge comprising two or more switching devices; a DC bus connected in parallel with the switching bridges; and a controller operable to control the switching bridges to control the power factor on the primary side of the hybrid distribution transformer and to reduce variations in the output voltage in the event of a change in the input voltage; wherein each of the first windings has a plurality of turns and a tap connected to one of the turns; wherein nodes in first, second and third ones of the switching bridges are connected to the taps of the first windings, respectively; wherein nodes in fourth, fifth and sixth ones of the switching bridges are connected to ends of the first windings, respectively; wherein a node in a seventh one of the switching bridges is connected to a bushing adapted for connection to the voltage source or the load; and wherein in each of the switching bridges, the node is located between the switching devices.

22. The hybrid distribution transformer of claim 21 , wherein the second windings are secondary windings for connection to the load and the bushing is an output bushing adapted for connection to the load.

23. A hybrid distribution transformer having a primary side for receiving input voltages and currents from a source and a secondary side for providing output voltages and currents to a load, the hybrid distribution transformer comprising: (a.) a ferromagnetic core; (b.) three winding assemblies mounted to the core, each winding assembly comprising a first, second and third windings, one of the first and second windings being a primary winding for connection to the voltage source and the other one of the first and second windings being a secondary winding for connection to the load, the third winding being an auxiliary primary winding or an auxiliary secondary winding; (c.) a single integrated voltage source converter connected to the second and third windings of each of the winding assemblies, the converter comprising: a first bridge comprising first, second and third circuit legs connected in parallel, each of the first, second and third circuit legs comprising a pair of semiconductor switches connected in series, wherein nodes in the first, second and third circuit legs are connected to ends of the third windings, respectively, and wherein in each of the first, second and third circuit legs, the node is located between the semiconductor switches; and a second bridge comprising fourth, fifth and sixth circuit legs connected in parallel, each of the fourth, fifth and sixth circuit legs comprising a pair of semiconductor switches connected in series, wherein nodes in the fourth, fifth and sixth legs are connected to ends of the second windings, respectively, and wherein in each of the fourth, fifth and sixth circuit legs, the node is located between the semiconductor switches; a DC bus connected in parallel with the first and second bridges; and (d.) a controller operable to control the converter to control the power factor on the primary side of the hybrid distribution transformer and to reduce variations in the output voltages in the event of changes in the input voltage.

24. The hybrid distribution transformer of claim 23 , wherein the DC bridge is connected between the first and second bridges and comprises a capacitor.

25. The hybrid distribution transformer of claim 23 , wherein the second bridge further comprises a seventh circuit leg comprising a pair of semiconductor switches connected in series, the seventh circuit leg being connected at a node to a bushing adapted for connection to the voltage source or the load, the node being located between the semiconductor switches.

26. The hybrid distribution transformer of claim 25 , wherein the second windings are main secondary windings for connection to the load, the third windings are auxiliary secondary windings and the bushing is an output bushing adapted for connection to the load.

27. The hybrid distribution transformer of claim 26 , wherein the third windings are connected in a Wye configuration, and wherein the first bridge further comprises an eighth circuit leg comprising a pair of semiconductor switches connected in series, the eighth circuit leg being connected at a node to a neutral of the Wye configuration, the node being located between the semiconductor switches.

28. The hybrid distribution transformer of claim 23 , further comprising sensors and an intelligent electronic device (IED) for monitoring the operation of the hybrid distribution transformer, the IED being connected to receive DC power from the DC bus and operable to receive operational data of the hybrid distribution transformer from the sensors, the operational data including currents, voltages and temperatures in the first and second windings.

29. The hybrid distribution transformer of claim 23 , wherein the IED comprises the controller and is connected to a remotely located control center by a communication link, the IED being operable to transmit the operational data to the control center and to receive commands for the controller from the control center.